1. Field of the Invention
The invention relates to a method for confirming the authenticity of a document.
The invention also relates to a device that is suitable for carrying out the method.
2. Related Technology
A prior-art method for generating digital signatures is offered by Deutsche Post AG under the trade designation Signtrust.
U.S. Pat. No. 4,405,829 discloses a method of asymmetrical cryptography. This known method serves for encrypting and digitally signing and thus confirming the authenticity and integrity of the digital document using a key pair. The asymmetry of the cryptographic method is achieved here by means of a primary factorization problem.
Moreover, it is a known procedure to use elliptical curves for the asymmetrical cryptography.
Furthermore, by using trust centers or a certificate authority, it is a known procedure to unambiguously associate a specific public key with a natural or legal person.
Moreover, standards exist regarding the association of the key and the execution of the method. Known standards are ISO/IEC IS X.509 and PKCS # 11.
Furthermore, methods for generating a secure hash value or a message digest are known. Here, a representative value is determined from a document or from parts of the document, said value serving as evidence of the authenticity of the document.
Moreover, it is a known procedure to integrate identification information into digital watermarks. This integration is done in such a way that the information can only be reconstructed with a key and it is otherwise imperceptible.
The article by S. Katzenbeisser and F. A. P. Petitcolas titled “Information Hiding Techniques for Steganography and Digital Watermarking,” Artech House, Norwood, Massachusetts, U.S.A., 2000, describes the linking of additional information, which is also referred to as metadata. The metadata, which is imperceptible without using auxiliary means, is inseparably linked to a digital document.
German Patent DE 195 219 69 C1 and European Patent EP 0 879 535 B1 describe a method for marking binarily encoded data records. Here, a data record to be marked is broken down into blocks of pixels, whereby the pixels are transformed from the configuration space to the frequency space by means of a transformation function. Furthermore, there is a discrete position sequence for the implementation of information units in the data records to be marked, taking into account a key as well as data-specific properties. The information unit to be implemented is written at the positions in the data record specified by the position sequence. As a result, the digital watermark is able to hold any binarily encoded information of variable length and to insert it into the document in a robust and forgery-proof manner.
International patent application publication WO 99/57885 and U.S. Pat. No. 6,243,480 describe a method for the digital confirmation of the authenticity of analog documents. With this method, the digital watermark that is embedded in the document serves as a carrier of authentication information. The displayed digital watermark survives media discontinuities. Moreover, this method discloses the use of a hash value as an authentication value.
German Preliminary Published Application DE 198 47 943 A1 describes a method for generating digital watermarks for electronic documents, whereby the genuine authorship of the documents is confirmed on the basis of digital watermarks. Here, in order to improve the possibility of identity confirmation, the watermark is provided with a hash value of the document.
Another known method for inserting a digital watermark is described in the article by R. G. van Schyndel, A. Z. Tirkel, C. F. Osborne titled “A Digital Watermark,” first IEEE International Conference on Image Processing, Vol. II, pp. 86-90. Austin, Tex., U.S.A., 1994. This method calls for the insertion of a digital watermark into an image in that the lowest-value bit of a pixel is changed and thus only minimal changes are inserted into the image. However, this known method has the drawback that the watermark can no longer be detected once the image has been manipulated or converted.
Here, it is especially important to apply the watermark in such a way that it is not destroyed through the manipulation or formatting of the document. A known procedure for solving this problem is to store information in the frequency space.
Fundamentally, however, other methods are also suitable for applying manipulation-proof watermarks, which are also known by the designation robust watermarks.
Moreover, methods are known that use machine-readable encoding to achieve the authentication of documents.
These methods use machine-readable bar codes and increase the forgery-proof character of certain documents, especially banknotes, checks, identification cards and lottery tickets. Such methods are described, for example, in international patent application publication WO 0007356.